The amino acid requirements of growing turkeys. 1. Model construction and parameter estimation

A model has been formulated to calculate the protein and amino acid requirements for growing turkeys. A requirement was taken as the sum of the needs for maintenance, for gain in carcass weight without feathers, and for the feathers. Parameters used in the model were obtained from a study of carcass composition along the growth period and from two balance trials with adult turkeys. The maintenance requirement was considered to be the sum of the needs for replacing skin and intestinal protein losses and for the obligatory creatinine excretion in the urine. Nitrogen retention was determined at 2.3 g/day in protein-fed adult (17 kg) male turkeys as an estimate for the replacement needs for skin protein loss. Creatinine excretion in these birds was 123 mg/day. When fed an N-free diet, 16.5 kg adult turkeys excreted a total of 3.5 g/day amino acids as a result of intestinal losses. The protein requirement for maintenance was estimated at 32 mg/day/g2/3 of body weight by summing up the different needs and dividing by .85, the coefficient of protein absorption. Protein and amino acid analyses of nude carcass and feathers and the growth curve were used to calculate the requirements for growth. These were then related to energy intake predicted by equations, which included previously determined coefficients for maintenance and growth (Hurwitz et al., 1980a), and the results of carcass lipid analysis. The calculated amino acid requirements were similar to those of the National Research Council (1977).